If the directional derivative Φ=axy^2+byz+cz^2x^3 at (-1,1,2) has maximum magnitude of 32 units

If the directional derivative Φ=axy^2+byz+cz^2x^3 at (-1,1,2) has maximum magnitude of 32 units

B. Tech.,B.E.,B.Sc.Mathematics:If the directional derivative of Phi=axy^2+byz+cz^2x^3 at (-1,1,2) has maximum magnitude of 32 units

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Find a,b,c so that directional derivative φ=axy^2+cz^2x^3+byz at (1,2,-1)max value 64 parallel to z
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Maths Tutorial 1 - Question 3, 4 and 5
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If the directional derivative Φ=axy^2+byz+cz^2x^3 at (-1,1,2) has maximum magnitude of 32 units